The (arcane) tricks to make vim or any editor work well is:

* export TERM=xterm-256color

* Use tmux attach -2 (-2=256color)

* In tmux <c-b>:set -g escape-time 0

* In vim, :set t_Co=256

If your terminal is the issue, use rxvt-unicode256color as it is the best terminal emulator (kitty is too slow (Python), urxvtd can segfault, xterm lacks features), or iTerm2 for Mac (Terminal.app recently broke colors and haven't figured out how to fix them, plus it lacks panes which I use to simulate an i3 environment). On Mac you have to enable option as meta key to make alt work as well